1. Field of the Invention:
The present invention relates to fans having fan impellers with flexible blades and, specifically, to fan impellers having blades constructed of flexible belting.
2. Description of the Prior Art:
Fans, turbines, blast wheels, and the like are known which feature impellers having flexible blades on a rotating shaft for moving fluids, such as air and other gases. For instance, U.S. Pat. No. 3,080,824 to Boyd, issued Mar. 12, 1963, shows a fluid-moving device with a rotating hub to which are attached flexible vanes. U.S. Pat. No. 1,868,113 to Ljungstrom, issued July 19, 1932, shows a table fan with flexible loop-shaped blades connected at opposite ends to a rotating hub.
Fan impellers using flexible belting for blades have several advantages. Since the belting is easily cut to a desired length, an infinite number of fan diameters can be provided on a hub assembly by simply cutting the belting blades to the length desired. This allows the fan to be adapted to utilize the motor horsepower efficiently, provides for changes in air volume or pressure requirements, and allows the fan to operate on different electrical power frequencies with the consequent changes in motor speeds which result. Fans with blades of flexible belting are also easier to insert and remove from within a fan housing through a relatively small opening, since the blades can be wrapped about the shaft or hub. This greatly simplifies the design of the fan housing as compared to the use of a rigid impeller. In spite of those disadvantages, the prior designs have all be deficient in some respect. One disadvantage of the prior flexible blade fan designs was that the flexible blades were typically attached to the rotating hub at one end only. For instance, each blade was typically made of a single piece of belting, with one end looped around a pin, or the like, and clamped to the hub of the impeller. Centrifugal force generated during operation of the fans acted at the point of attachment and tended to cause the flexible blade to tear or separate. In the case of a fan impeller such as those used in cotton ginning where the fan moves dirty air with abrasive particles, the flexible blades are typically used on a 60 to 70 horsepower motor having a blade diameter of 18 to 20 inches which operates in the neighborhood of 2200 rpm. The centrifugal force generated by such fans is sufficient to cause early blade failure in prior fan designs.